Recruitment, Ecology, Growth and Behavior of Juvenile Acanthaster Planci (L.) (Echinodermata: Asteroidea)

On Suva Reef in the Fiji Islands the refuge substratum of early juvenile A. planei (<20 mm) was found to be subtidal coralline algae (Porolithon onkodes) on the windward reef front. Highly cryptic juveniles (10–30 mm maximum diameter) were found under coral blocks and rubble in the boulder zone of exposed reef fronts, on the dead bases of Acropora spp. in more sheltered areas, and in interstices on the reef crest and on the fore reef slope to depths of 8 m. Recruitment, monitored over 9 years, was very low in most years (in 1985 the density of 8-month-old juveniles was 0.004 m⁻² in the boulder zone). A massive recruitment occurred in 1984 (density of 7-month-old juveniles was 8.3 m⁻² in the boulder zone). Monitoring of this cohort over 2 years indicated that growth was sigmoidal. The maximum diameter increased by 2.6, 16.7 and 5.3 mm/month in the algal-feeding, early coral-feeding and adult phases, respectively. An epidemic caused a high mortality between 10–16 months. The diet switched from coralline algae to scleractinian corals at age 13–15 months but behavior remained cryptic. At about 20 months feeding switched from night to day and aggregative behavior began. The onset of sexual maturity commenced at 23 months. Between 26 and 28 months the population migrated into the deeper waters of the reef slope. Mortality between ages 8 and 23 months was very high (ca. 99%) and is attributed to disease, and possibly the effects of rough seas and predation. These findings indicate that recruitment is erratic and that an infestation arises from a single massive settlement.